The impact of executive dysfunctions on Theory of Mind abilities in Parkinson's disease.

Theory of Mind (ToM) is the ability to infer and reason about others' mental states, a process impaired by Parkinson's disease (PD). ToM performance in PD seems to be strongly related to executive functioning but the exact nature of this relationship is still unclear. We aim to investigate the direct impact of several executive dysfunctions on ToM deficits (Affective and Cognitive ToM) in PD patients. Sixty-eight PD patients underwent neuropsychological tests evaluating executive control such as inhibition, cognitive flexibility, processing speed or working memory and Cognitive and Affective ToM. We divided participants into two groups based on their performance on executive tests: PD patients with poor executive functioning (PD-EF-) and those with preserved executive functioning (PD-EF+). To explore the direct impact of executive subdomains on ToM abilities, two mediation models were executed in the whole sample. We found that PD patients with poor executive functioning reported poorer scores on Affective and Cognitive ToM tasks than PD patients with preserved executive functions, controlling for age and education. Moreover, parallel mediation models, conducted in the whole sample, indicated that performance on phonological fluency mediated the relationships between educational level and both Affective and Cognitive ToM, controlling the effect of other executive tests. These findings further support the idea that executive functions are crucial in ToM processes. Particularly, phonological fluency, whose execution requires both verbal abilities and cognitive flexibility, mediated ToM performance controlling the effect of other executive functions. The identification of neuropsychological processes underpinning ToM abilities might represent a plausible target for cognitive training to strengthen ToM abilities in PD.